1. Field of the Invention
The present invention relates generally to a cooling arrangement for a piston head of an internal combustion engine. More specifically, the invention relates to a cooling arrangement for a piston head, which can effectively cool the piston head at various engine cycle positions.
2. Description of the Background Art
As is well known, a piston head is an engine part which is directly exposed to an engine combustion chamber to receive combustioning pressure for transmitting force generated by combustion to a crankshaft via a piston rod. Therefore, the piston head is constantly subject to substantially high heat in the combustion chamber. The piston head is thus required to be effectively cooled to expand lift and optimize engine performance. In order to cool the piston head, there has been proposed a piston head which is formed with a cooling channel therein. A lubricating oil is introduced into the cooling channel by injection through a lubricant injection nozzle which is disposed in an engine cylinder through an engine cylinder block. Such an arrangement is provided for effectively cooling the top portion of the piston head, which is directly subject to high heat in the engine combustion chamber.
In this type of piston head cooling arrangement, it is important to effectively introduce the lubricating oil into the cooling channel. As can be appreciated, the position of the piston head varies between the top-dead-center (TDC) and the bottom-dead center (BDC) according to an engine revolution cycle. A difficulty is thus encountered in effectively introducing the lubricating oil into the cooling channel at various positions of the piston head. Namely, if the lubricant injection nozzle is facilitated to inject the lubricating oil for effective introduction into the cooling channel at the BDC of the piston head, the axis of flow of the injected lubricating oil will be offset from the axis of a lubricant induction path for the cooling channel at the TDC of the piston head. As a result, induction efficiency of the lubricating oil at the TDC can be lowered thereby causing a lowering of cooling efficiency.
In order to overcome this difficulty, Japanese Utility Model First (unexamined) Publication (Jikkai) Showa 61-144242 proposes a multi-nozzle system which has a plurality of lubricant injection nozzles. Namely, according to the disclosed embodiment, there is provided first and second lubricant injection nozzles. The first and second lubricant injection nozzles are active for injecting the lubricating oil at specific piston positions, e.g. at or in the vicinity of the BDC, so that an increased amount of the lubricating oil can be introduced into the cooling channel so that the cooling efficiency for the piston head can be maintained at an acceptable level.
Such an arrangement provides some improvement in the piston head cooling technology for effective cooling of the piston head. However, on the other hand, such arrangement requires a plurality of lubricant injection nozzles. Furthermore, the lubricant nozzles are required to be arranged at positions for effectively introducing the lubricating oil to respectively corresponding cooling channels at the specific piston stroke position. Therefore, construction of the cooling arrangement becomes complicated and difficulty in production and assembly are encountered.